The present invention is directed to improved functional release agents for the fusing of electrostatic toner particles. More specifically, the present invention is directed to a functional polysiloxane fuser release agent with improved thermal stability. One embodiment of the present invention is directed to a composition comprising a mixture of (a) a primary- or secondary-amino-functionalized polyorganosiloxane oil and (b) a compound which is a low molecular weight, non-sterically-hindered aldehyde or ketone. Another embodiment of the present invention is directed to a fusing release agent comprising the reaction product of (a) a primary- or secondary-amino-functionalized polyorganosiloxane oil and (b) a compound which is a low molecular weight, non-sterically-hindered aldehyde or ketone.
In a typical electrostatographic reproducing apparatus, a light image of an original to be copied is recorded in the form of an electrostatic latent image upon a photosensitive member, and the latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin particles and pigment particles, or toner. The visible toner image is then in a loose powdered form and can be easily disturbed or destroyed. The toner image is usually fixed or fused upon a support, which can be the photosensitive member itself, or some other support sheet such as plain paper.
The use of thermal energy for fixing toner images onto a support member is well known. To fuse electroscopic toner material onto a support surface permanently by heat, it is usually necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky. This heating causes the toner to flow to some exten into the fibers or pores of the support member. Thereafter, as the toner material cools, solidification of the toner material causes the toner to be bonded firmly to the support.
Typically, the thermoplastic resin particles are fused to the substrate by heating to a temperature of from about 90xc2x0 C. to about 200xc2x0 C. or higher, depending on the softening range of the particular resin used in the toner. It may be undesirable, however, to increase the temperature of the substrate substantially higher than about 250xc2x0 C. because of the tendency of the substrate to discolor or convert into fire at such elevated temperatures, particularly the substrate is paper.
Several approaches to thermal fusing of electroscopic toner images have been described. These methods include providing the application of heat and pressure substantially concurrently by various means, a roll pair maintained in pressure contact, a belt member in pressure contact with a roll, a belt member in pressure contact with a heater, and the like. Heat can be applied by heating one or both of the rolls, plate members, or belt members. Fusing of the toner particles occurs when the proper combination of heat, pressure, and/or contact for the optimum time period are provided. The balancing of these variables to bring about the fusing of the toner particles is well known in the art, and can be adjusted to suit particular machines or process conditions.
During the operation of one fusing system in which heat is applied to cause thermal fusing of the toner particles onto a support, both the toner image and the support are passed through a nip formed between a pair of rolls, plates, belts, or combination thereof. The concurrent transfer of heat and the application of pressure in the nip effects the fusing of the toner image onto the support. It is important in the fusing process that minimal or no offset of the toner particles from the support to the fuser member takes place during normal operations. Toner particles offset onto the fuser member can subsequently transfer to other parts of the machine or onto the support in subsequent copying cycles, thereby increasing the image background, causing inadequate copy quality, causing inferior marks on the copy, or otherwise interfering with the material being copied there as well as causing toner contamination of other parts of the machine. The referred to xe2x80x9chot offsetxe2x80x9d occurs when the temperature of the toner is increased to a point where the toner particles liquefy and a splitting of the molten toner takes place during the fusing operation with a portion remaining on the fuser member. The hot offset temperature or degradation of the hot offset temperature is a measure of the release properties of the fuser member, and accordingly it is desirable to provide a fusing surface having a low surface energy to provide the necessary release.
To ensure and maintain good release properties of the fuser member, it has become customary to apply release agents to the fuser member during the fusing operation. Typically, these materials are applied as thin films of, for example, silicone oils, such as polydimethyl siloxane, or substituted silicone oils, such as amino-substituted oils, mercapto-substituted oils, or the like, to prevent toner offset. In addition, fillers can be added to the outer layers of fuser members to increase the bonding of the fuser oil to the surface of the fuser member, thereby imparting improved release properties.
The use of polymeric release agents having functional groups which interact with a fuser member to form a thermally stable, renewable self-cleaning layer having good release properties for electroscopic thermoplastic resin toners, is described in, for example, U.S. Pat. Nos. 4,029,827, 4,101,686, and 4,185,140, the disclosures of each of which are totally incorporated herein by reference. Disclosed in U.S. Pat. No. 4,029,827 is the use of polyorganosiloxanes having mercapto functionality as release agents. U.S. Pat. Nos. 4,101,686 and 4,185,140 are directed to polymeric release agents having functional groups such as carboxy, hydroxy, epoxy, amino, isocyanate, thioether, and mercapto groups as release fluids.
It is important to select the correct combination of fuser surface material, any filler incorporated or contained therein, and fuser oil. Specifically, it is important that the outer layer of the fuser member react sufficiently with the selected fuser oil to obtain sufficient release. To improve the bonding of fuser oils with the outer surface of the fuser member, fillers have been incorporated into or added to the outer surface layer of the fuser members. The use of a filler can aid in decreasing the amount of fusing oil necessary by promoting sufficient bonding of the fuser oil to the outer surface layer of the fusing member. It is important, however, that the filler not degrade the physical properties of the outer layer of the fuser member, and it is also important that the filler not cause too much of an increase in the surface energy of the outer layer.
Fillers are also sometimes added to the outer layers of fuser members to increase the thermal conductivity thereof. Examples of such fillers include conductive carbon, carbon black, graphite, aluminum oxide, titanium, and the like, as well as mixtures thereof. Efforts have been made to decrease the use of energy by providing a fuser member which has excellent thermal conductivity, thereby reducing the temperature needed to promote fusion of toner to paper. This increase in thermal conductivity also allows for increased speed of the fusing process by reducing the amount of time needed to heat the fuser member sufficiently to promote fusing. Efforts have also been made to increase the toughness of the fuser member layers to increase abrasion resistance and, accordingly, the life of the fuser member.
With regard to known fuser coatings, silicone rubber has been the preferred outer layer for fuser members in electrostatographic machines. Silicone rubbers interact well with various types of fuser release agents. Perfluoroalkoxypolytetrafluoroethylene (PFA Teflon), however, which is frequently used as an outer coating for fuser members, is more durable and abrasion resistant than silicone rubber coatings. Also, the surface energy for PFA Teflon is lower than that of silicone rubber coatings.
U.S. Pat. No. 5,864,740 (Heeks et al.), the disclosure of which is totally incorporated herein by reference, discloses a thermally stabilized silicone liquid composition and a toner fusing system using the thermally stabilized silicone liquid as a release agent, wherein the thermally stabilized silicone liquid contains a silicone liquid and a thermal stabilizer composition (including a reaction product from at least a polyorganosiloxane and a platinum metal compound (Group VIII compound) such as a ruthenium compound, excluding platinum.
U.S. Pat. No. 5,531,813 (Henry et al.), the disclosure of which is totally incorporated herein by reference, discloses a polyorgano amino functional oil release agent having at least 85 percent monoamino functionality per active molecule to interact with the thermally stable FKM hydrofluoroelastomer surface of a fuser member of an electrostatographic apparatus to provide an interfacial barrier layer to the toner and a low surface energy film to release the toner from the surface.
U.S. Pat. No. 5,516,361 (Chow et al.), the disclosure of which is totally incorporated herein by reference, discloses a fusing system, a method of fusing, and a fuser member having a thermally stable FKM hydrofluoroelastomer surface for fusing thermoplastic resin toners to a substrate in an electrostatographic printing apparatus, said fuser member having a polyorgano T-type amino functional oil release agent. The oil has predominantly monoamino functionality per active molecule to interact with the hydrofluoroelastomer surface to provide a substantially uniform interfacial barrier layer to the toner and a low surface energy film to release the toner from the surface.
U.S. Pat. No. 5,512,409 (Henry et al.), the disclosure of which is totally incorporated herein by reference, discloses a method of fusing thermoplastic resin toner images to a substrate in a fuser including a heated thermally stable FKM hydrofluoroelastomer fusing surface at elevated temperature prepared in the absence of anchoring sites for a release agent of heavy metals, heavy metal oxides, or other heavy metal compounds forming a film of a fluid release agent on the elastomer surface of an amino functional oil having the formula 
where 50xe2x89xa6nxe2x89xa6200, p is 1 to 5, R1, R2, and R3 are alkyl or arylalkyl radicals having 1 to 18 carbon atoms, R4 is an alkyl or arylalkyl radical having 1 to 18 carbon atoms and a polyorganosiloxane chain having 1 to 100 diorganosiloxy repeat units, and R5 is a hydrogen, alkyl, or arylalkyl radical having 1 to 18 carbon atoms, the oil having sufficient amino functionality per active molecule to interact with the hydrofluoroelastomer surface in the absence of a heavy metal and heavy metal anchoring sites to provide an interfacial barrier layer to the toner and a low surface energy film to release the toner from the surface. The process entails contacting the toner image on the substrate with the filmed heated elastomer surface to fuse the toner image to the substrate and permitting the toner to cool.
U.S. Pat. No. 5,493,376 (Heeks), the disclosure of which is totally incorporated herein by reference, discloses a thermally stabilized polyorganosiloxane oil including a polyorganosiloxane oil and, as the thermal stabilizer, the reaction product of chloroplatinic acid and a member selected from the group consisting of a cyclic polyorganosiloxane having the formula 
where R3 is an alkyl radical having 1 to 6 carbon atoms and R4 is selected from the group consisting of alkene and alkyne radicals having 2 to 8 carbon atoms, and n is from 3 to 6; a linear polyorganosiloxane having the formula 
wherein R1 and R2 are selected from the group consisting of hydroxy and alkyl, alkoxy, alkene, and alkyne radicals having 1 to 10 carbon atoms, provided that at least one of R1 and R2 is alkene or alkyne, and m is from 0 to 50; and mixtures thereof, present in an amount to provide at least 5 parts per million of platinum in said oil.
U.S. Pat. No. 5,401,570 (Heeks et al.), the disclosure of which is totally incorporated herein by reference, discloses a fuser member comprising a substrate and thereover a silicone rubber containing a filler component therein, wherein the filler component is reacted with a silicone hydride release oil.
U.S. Pat. No. 5,395,725 (Bluett et al.), the disclosure of which is totally incorporated herein by reference, discloses a process for fusing toner images to a substrate which comprises providing a fusing member having a fusing surface; heating the fuser member to an elevated temperature to fuse toner to the substrate; and applying directly to the fusing surface a fuser release agent oil blend composition; wherein volatile emissions arising from the fuser release agent oil blend are minimized or eliminated.
U.S. Pat. No. 5,157,445 (Shoji et al.), the disclosure of which is totally incorporated herein by reference, discloses a fixing device where a copying medium carrying a nonfixed toner image thereon is passed between a pair of fixing rolls as being kept in direct contact with each other under pressure so as to fix the nonfixed toner image on the copying medium, the device being characterized in that a toner release at least containing, as an active ingredient, a functional group containing organopolysiloxane of the general formula 
the organopolysiloxane having a viscosity of from 10 to 100,000 cs at 25xc2x0 C., is supplied to at least the fixing roll of being brought into contact with the nonfixed toner image of the pair of fixing rolls. Using the toner release, the copying medium releasability from the fixing roll to which the toner release is applied is good and the heat resistance of the fixing roll is also good.
U.S. Pat. No. 4,515,884 (Field et al.), the disclosure of which is totally incorporated herein by reference, discloses the fusing of toner images to a substrate, such as paper, with a heated fusing member having a silicone elastomer fusing surface by coating the elastomer fusing surface with a toner release agent which includes an unblended polydimethyl siloxane having a kinematic viscosity of from about 7,000 to about 20,000 centistokes. In a preferred embodiment the polydimethyl siloxane oil has a kinematic viscosity of from about 10,000 to about 16,000 centistokes and the fuser member is a fuser roll having a thin layer of a crosslinked product of a mixture of xcex1,xcfx89-dihydroxypolydimethyl siloxane, finely divided tabular alumina, and finely divided iron oxide.
U.S. Pat. No. 4,185,140 (Strella et al.), the disclosure of which is totally incorporated herein by reference, discloses polymeric release agents having functional groups such as carboxy, hydroxy, epoxy, amino, isocyanate, thioether, or mercapto groups which are applied to a heated fuser member in an electrostatic reproducing apparatus to form thereon a thermally stable, renewable, self-cleaning layer having excellent toner release properties for conventional electroscopic thermoplastic resin toners. The functional polymeric fluids interact with the fuser member in such a manner as to form a thin, thermally stable interfacial barrier at the surface of the fuser member while leaving an outer film or layer of unreacted release fluid. The interfacial barrier is strongly attached to the fuser member surface and prevents electroscopic thermoplastic resin toner material from contacting the outer surface of the fuser member. The material on the surface of the fuser member is of minimal thickness and thereby represents a minimal thermal barrier.
U.S. Pat. No. 4,150,181 (Smith), the disclosure of which is totally incorporated herein by reference, discloses a contact fuser assembly and method for preventing toner offset on a heated fuser member in an electrostatic reproducing apparatus which includes a base member coated with a solid, abrasion resistant material such as polyimide, poly(amide-imides), poly(imide-esters), polysulfones, and aromatic polyamides. The fuser member is coated with a thin layer of polysiloxane fluid containing low molecular weight fluorocarbon. Toner offset on the heated fuser member is prevented by applying the polysiloxane fluid containing fluorocarbon to the solid, abrasion resistant surface of the fuser member.
U.S. Pat. No. 4,146,659 (Swift et al.), the disclosure of which is totally incorporated herein by reference, discloses fuser members having surfaces of gold and the platinum group metals and alloys thereof for fuser assemblies in office copier machines. Preferred fuser assemblies include cylindrical rolls having at least an outer surface of gold, a platinum group metal, or alloys thereof. Electroscopic thermoplastic resin toner images are fused to a substrate by using a bare gold, a platinum group metal, or alloys thereof fuser member coated with polymeric release agents having reactive functional groups, such as a mercapto-functional polysiloxane release fluid.
U.S. Pat. No. 4,101,686 (Strella et al.), the disclosure of which is totally incorporated herein by reference, discloses polymeric release agents having functional groups such as carboxy, hydroxy, epoxy, amino, isocyanate, thioether, or mercapto groups. The release agents are applied to a heated fuser member in an electrostatic reproducing apparatus to form thereon a thermally stable, renewable, self-cleaning layer having excellent toner release properties for conventional electroscopic thermoplastic resin toners. The functional polymeric fluids interact with the fuser member in such a manner as to form a thin, thermally stable interfacial barrier at the surface of the fuser member while leaving an outer film or layer of unreacted release fluid. The interfacial barrier is strongly attached to the fuser member surface and prevents electroscopic thermoplastic resin toner material from contacting the outer surface of the fuser member. The material on the surface of the fuser member is of minimal thickness and thereby represents a minimal thermal barrier.
U.S. Pat. No. 4,046,795 (Martin), the disclosure of which is totally incorporated herein by reference, discloses a process for preparing thiofunctional polysiloxane polymers which comprises reacting a disiloxane and/or a hydroxy or hydrocarbonoxy containing silane or siloxane with a cyclic trisiloxane in the presence of an acid catalyst wherein at least one of the organosilicon compounds contain a thiol group. These thiofunctional polysiloxane polymers are useful as metal protectants and as release agents, especially on metal substrates.
U.S. Pat. No. 4,029,827 (Imperial et al.), the disclosure of which is totally incorporated herein by reference, discloses polyorgano siloxanes having functional mercapto groups which are applied to a heated fuser member in an electrostatic reproducing apparatus to form thereon a thermally stable, renewable, self-cleaning layer having superior toner release properties for electroscopic thermoplastic resin toners. The polyorgano siloxane fluids having functional mercapto groups interact with the fuser member in such a manner as to form an interfacial barrier at the surface of the fuser member while leaving an unreacted, low surface energy release fluid as an outer layer or film. The interfacial barrier is strongly attached to the fuser member surface and prevents toner material from contacting the outer surface of the fuser member, the material on the surface of the fuser member is of minimal thickness and thereby represents a minimal thermal barrier The polyorgano siloxanes having mercapto functionality have also been effectively demonstrated as excellent release agents for the reactive types of toners having functional groups thereon.
U.S. Pat. No. 4,011,362 (Stewart), the disclosure of which is totally incorporated herein by reference, discloses metal substrates such as molds and fuser rolls which are coated with carboxyfunctional siloxanes to improve their release characteristics.
U.S. Pat. No. 3,731,358 (Artl), the disclosure of which is totally incorporated herein by reference, discloses a silicone rubber roll for pressure fusing of electrostatically produced and toned images at elevated temperatures. The roll inherently prevents offset of the image by supplying a release material to the surface of the roll. When the release material is depleted, the roll can be restored by impregnation with silicone oil.
U.S. Pat. No. 3,002,927 (Awe et al.), the disclosure of which is totally incorporated herein by reference, discloses organosilicon fluids capable of withstanding high temperatures which are prepared by preoxygenating the fluid by heating a mixture of (1) a polysiloxane fluid in which the siloxane units are selected from the group consisting of units of the formula R3SiO0.5, R2SiO, RSiO1.5, and SiO2 in which each R is selected from the group consisting of methyl, phenyl, chlorophenyl, fluorophenyl, and bromophenyl radicals, (2) a ferric salt of a carboxylic acid having from 4 to 18 carbon atoms in an amount such that there is from 0.005 to 0.03 percent by weight iron based on the weight of (1), and (3) oxygen mechanically dispersed in the fluid at a temperature above 400xc2x0 F. until the mixture changes to a reddish brown color and until the mixture will not form a precipitate when heated in the absence of oxygen at a temperature above that at which the preoxygenation step is carried out.
With regard to known fusing oils, silicone oil has been the preferred release agent for PFA Teflon coatings for fuser members. Release agents comprising silicone oil, however, do not provide sufficient release properties for toner because the silicone oil does not wet fuser coatings of PFA Teflon. Therefore, a large amount (greater than 5 mg/copy) of silicone oil is required to obtain minimum release performance. Alternatively, a large amount of wax must be incorporated into the toner in order to provide adequate release of the toner from the fuser member.
For other fluoropolymer, and especially fluoroelastomer, fuser member outer layers, amino silicone oil has been the release agent of choice. Amino oil, however, does not diffuse into paper products, but instead reacts with the cellulose in the paper and therefore remains on the surface of the paper. It is believed that hydrogen bonding occurs between the amine groups in the amino oil and the cellulose hydroxy groups of the paper. Alternatively, the amine groups can hydrolyze the cellulose rings in the paper. The amino oil on the surface of the copied paper prevents the binding of glues and adhesives, including attachable notes such as adhesive 3M Post-it(copyright) notes, to the surface of the copied paper. In addition, the amino silicone oil present on the surface of a copied paper prevents ink adhesion to the surface of the paper. This problem results in the poor fix of inks such as bank check endorser inks and other similar inks.
Amino polyorganosiloxane oils also undergo degradation at a much faster rate than nonfunctional polyorganosiloxane oils. Particularly when the oil is heated in the sump of the fusing apparatus, it is believed that the amino functional groups undergo thermal oxidative degradation and convert to the reduced form after a period of time. Accordingly, after the oil has been heated in the sump for an extended period of time, the amine functionality of the oil (mole percent of amino groups in the polymer) is reduced by the time it is introduced into the fusing nip. This difficulty cannot be overcome by raising the beginning amine functionality of the oil, because increasing the number of amino groups on the polymer by too great an amount can lead to gellation.
While known compositions and processes are suitable for their intended purposes, a need remains for improved fuser release agents. In addition, a need remains for amino-functional polyorganosiloxane fuser release agents with improved thermal stability. Further, a need remains for amino-functional polyorganosiloxane fuser release agents with improved resistance to oxidative attack. Additionally, a need remains for amino-functional polyorganosiloxane fuser release agents that have the desired degree of amino functionality when they enter the fusing nip, even after the fuser release agent has been heated for an extended period of time. There is also a need for functional polyorganosiloxane fuser release agents that exhibit improved interactions with paper. In addition, there is a need for functional polyorganosiloxane fuser release agents that exhibit increased useful lifetimes. Further, there is a need for functional polyorganosiloxane fuser release agents that improve the useful lifetimes of fuser members.
The present invention is directed to a composition comprising a mixture of (a) a primary- or secondary-amino-functionalized polyorganosiloxane oil and (b) a compound which is a low molecular weight, non-sterically-hindered aldehyde or ketone. Another embodiment of the present invention is directed to a fusing release agent comprising the reaction product of (a) a primary- or secondary-amino-functionalized polyorganosiloxane oil and (b) a compound which is a low molecular weight, non-sterically-hindered aldehyde or ketone.